Protective device for electric circuits.



A. v. A. McHARG. I PROTECTIVE DEVICE FOR ELECTRIC CIRCUITS. APPLICATIONFILED NOV. 28,1918.

1,120,212. Patented Dec. 8, 1914.

UNITED STATES PATENT OFFICE.

ARTHUR v. A. McHARG, or NEW YoRK, N. Y., ASSIGNOR TO THOMAS E. MURRAY,or NEW YORK, N. Y.

Specification of Letters Patent.

Patented Dec. 8, 1914.

. Application filed November 28, 1913. Serial No. 803,521.

To all whom it may concern:

Be it lmown that I, ARTHUR V. A. Mo- HARG, a citizen of the UnitedStates, residing at New York, in the county of New York and State of NewYork, have invented a certain new and useful Improvement in ProtectiveDevices for Electric Circuits, of which the following is aspecification.

The invention is a protective device for electric circuits. It embodiesa novel principle, namely, interrupting an electric circuit bydestroying by heat electrically generated in said circuit, a body ofdestructible material, by means of which body terminals of said circuitare held in contact, and thereby permitting said terminals to separateand break said circuit. This principle may be embodied in many differentforms of ap paratus. I herein illustrate one practical and eflicientform wherein a movable switch member normally retracted by a spring isheld in circuit closing position against the resiliency of said springby means of a fuse or stop of material destructible by heat, whlch stopis then in contact with a con- (luctor mounted on said switch member andin circuit. Upon the development of an overload current on the circuit,said conduo-tor becomes heated and in turn heats and so destroys thestop. The switch member then being released is retracted to open circuitby the spring. In this way, the circuit is protected from theefl'ects'of said overload current by a fuse or body of destructiblematerial which is not in the circuit.

In the accompanying drawingsFigure 1 is a longitudinal section of myprotective device on the line w, m of Fig. 2. Fig. 2 is a horizontalsection on the line 3 y of Fig. 1. Fig. 3 is an elevation of thebridge-carrying extremity of the switch lever. Fig. 4 is a Ifnodifiedform of the destructible stop or ise.

Similar numbers of reference indicate like parts.

1 is a base of insulating material, 2 is a switch lever also ofinsulating material. Upon the upper side of said lever is a metal plate3, integral with which are lateral side ieces 4 which are bent over andreceive the liody of the switch lever between them. The lever issupported on a shaft 5 of insulating material journaled in plates 6.secured to the base 1, with which plates the side pieces 4. makecontact. On the under side of lever 1 near the end thereof is astirrup-shaped plate 7. When the lever is in circuit-closing position,as shown in Fig. 1, the plate 7 enters between the arms of a contactclip 8 secured to base 1. Extending outwardly fr om the end of lever 2is a bridge conductor 2 in loop form. One end of said conductor is 1nelectrical contact with plate 3. The

' other end is in electrical contact with the front edges of plate 7,said end being widsued to extend across said edges and being secured inplace by the screw 10 entering lever 2, as shown in Fig. 3.

11 is a standard having a threaded recess in its upper end to receivethe head of screw 12, which enters base 1. Between the shank of screw 12and standard 11 is a clearance so that said standard may freely turn onsaid shank. The recess in standard 11 is interiorly threaded to receivethe screw plug 13 which is on the end of an insulating rod 14. Rod 14has a flange l5 and at its upper end a head 16 by which it can be rotaied. The standard 11 supports a toothed disk 17 of fusible metal or othermaterial destructible by heat, which disk has a central opening toreceive the plug 13, so that when the plug is in place, the disk isclamped between the flange 15 and the top of standard 11.

On the switch lever 2 is an upwardly extending arm 18, to which isattached one end of the helical retracting spring 19, the other end ofsaid spring being secured to base 1. Circuit wires 21, 20 arerespectively connected to plates 6 and clip 8. A boxshaped cover 22 isprovided having an opening for the passage of the head 16 and a slot inone of its walls and extending to the edge thereof for the admission ofshaft 5. This slot is closed when the cover is in place by a plate 23secured on the base 1 and provided on its upper edge with a semicircularrecess receiving shaft 5. A handle 25 is secured on the end of shaft 5which projects outside of the cover.

The operation is as follows: The cover being preferably removed, thescrew plug 13 is Withdrawn from the standard 11, the disk 17 is put inplace on said standard, and the plug 13 is reinserted to clamp the disk17 firmly between the standard and flange 15. The lever 2 is thenbrought into circuit closing position, the bridge 9 passing through oneof the spaces between the projections on the disk. The lever beingretained in thisv position by the operator, the head 16 is rotated untilone of said projections '24 comes directly above the bridge 9. The leveris then released, but is held from rising under the pull of spring 19 bythe projection 2% with which the bridge 9 becomes held'in contact. Thebridge 9 is to be so proportioned as that it will conduct apredetermined normal current without becoming hot enough to fuse ordestroy the holding projection, but to become heated to a sufficientdegree to destroy said projection upon the occurrence of any selectedoverload current. To this end, it may be made of higher resistance thanthe rest of the circuit. The destruction of said holding projection thenreleases lever 2 which is immediately thrown up, as indicated in dottedlines, Fig. '1, out of clip 8 by the action of spring 19, thus "breakingthe .circuit and so protecting any devicestherein included from theeifects of said increased current.

In order to reset the apparatus, the disk 17 is rotated by head 16 untilanother projection on said disk comes into position toengage bridge 9,and obviously the resetting may be repeated as many times as there areprojections on said disk. When all of said projections have in turn beendestroyed, a

new disk is to be substituted.

wires comes directly over the bridge 9, and

acts as a stop to prevent retraction of the lever. by spring 19. Thiswire on the occurrence of an overload current becomes fused, releasingthe lever, as alreadydescribed.

ll claim:

1. A fixed circuit terminal, a'movable circuit terminal cooperatingtherewith, resilient retracting means. for said movable teral,'aplurality of devices for holding ma am said movable terminal inpredetermined position with reference to said fixed terminal against theresiliency of said retracting means, means for moving said devicessuccessively into engagement with said movable terminal, and means forheating said devices to destroy the same to release said movableterminal 2. A fixed circuit terminal, a movable circuit terminal'cocperating therewith, resilicut retracting means for said movableterminal, a plurality of stops for holding said movable terminal inpredetermined position with reference to said fixed terminal against theresiliency of said retracting means, means for moving said stopssuccessively into engagement with said movable terminal, and meanscontrolled by an overload current on said circuit for destroying saidstops.

3. A movable switch member divided into two mutually insulated sections,resilient retracting means therefor, a bridge of conducting material ofhigher resistance than said sections and connecting said sections, andmeans in contact with said bridge for holding said memberin circuitclosing position against the resiliency of said spring; the said holdingmeans, upon the heating of said bridge by current on said circuit, beingdestructible to release said movable member to open said switch.

4. A movable switch member divided into two mutually insulated sections,resilient retracting .means therefor, a bridge of conducting material ofhigher resistance than said sections: connecting .said sections andprojecting front-mid switch member, and a stop in contact with saidbridge for holding said member in circuit closing position againsttheresiliency of said spring; the said.stop, uponthe heating ofsaidbridge by current on said circuit, being fusible to release saidmovable member to open said switch.

In testimony whereof I have afixed my signature in presence of twowitnesses.

T3HUR V. A. Moi ii Witnesses:

' Gnnrnunn T. PORTER,

YT. McGr.

